(1) Field of the Invention
This invention relates to a method for producing .alpha.-(p-isobutylphenyl)propionic acid or its alkyl esters. More particularly, the invention relates to a novel method for economically producing the above compounds in a pure form.
As disclosed in British Pat. No. 971,700 and French Pat. No. 1,549,758, .alpha.-(p-isobutylphenyl)propionic acid (hereinafter referred to as "IPA") is known as a useful medicine for the relief of pain, fever and inflammation.
(2) Description of the Prior Art
IPA and its alkyl esters (hereinafter referred to as "IPE" have been synthesized from various kinds of starting materials by several methods.
In order to prepare IPA and IPE in a pure form at low cost, the following conditions are required
(a) To use simple compounds as starting materials;
(b) To employ a series of reactions in which intermediate compounds are also simple and stable;
(c) To employ reactions that do not cause isomerization because the isobutyl group is liable to be isomerized; and
(d) To use inexpensive reagents and catalysts.
In the methods for synthesizing IPA or IPE as disclosed in U.S. Pat. Nos. 3,385,886; 3,385,887 and 4,329,507, however, intricate and expensive substances are used as starting materials or unstable and intractable reagents such as Grignard reagents are used so that these methods cannot be regarded as inexpensive and economical.
Furthermore, in the methods disclosed in French Pat. No. 1,549,758 and the above U.S. Patents, p-isobutylacetophenone is used as a starting material.
The p-isobutylacetophenone, however, is not an inexpensive compound as described below. It is most economical to synthesize the p-isobutylacetophenone from isobutylbenzene but the conversion itself of isobutylbenzene into p-isobutylacetophenone is not desirable in an economical view point. That is, an expensive and unstable material of acetyl chloride must be used in the conversion into p-isobutylacetophenone. In addition, a large quantity of, i.e. at least equimolecular amount (to acetyl chloride) of anhydrous aluminum chloride that is quite susceptible to moisture, must be used. For example, assuming that the conversion rate is stoichiometrically 100%, anhydrous aluminum chloride as much as 700 kg is to be used for producing 1,000 kg of p-isobutylacetophenone. In addition, waste materials of 410 kg of aluminum hydroxide and 750 kg of chlorine ions are produced as a result of the deactivation of anhydrous aluminum chloride and the waste materials that exceed the quantity of aimed p-isobutylacetophenone must be treated into innoxious substances. Accordingly, it goes without saying that p-isobutylacetophenone is quite expensive as a starting material. Furthermore, the conversion from p-isobutylacetophenone into .alpha.-(p-isobutylphenyl)propionaldehyde must be done via intricate intermediate compounds which is not economical in an industrial viewpoint.